Non-reciprocal circuit element, method for manufacturing the same, and communication device

ABSTRACT

A non-reciprocal circuit element is equipped with a ferrite-magnet assembly which includes a pair of permanent magnets and a ferrite sandwiched between the permanent magnets. A first center electrode and a second center electrode defined by conducting films are provided on principal surfaces of the ferrite, such that the first center electrode and the second center electrode are insulated from each other and intersect each other. The permanent magnets have principal surfaces having substantially the same shape as the principal surfaces of the ferrite. The ferrite has upper and lower surfaces provided with recesses. The recesses have a conductor material embedded therein, whereby intermediate electrodes and connector electrodes are provided.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to non-reciprocal circuit elements, andparticularly, to a non-reciprocal circuit element, such as an isolatorand a circulator, for use in microwave bands, to a method formanufacturing the non-reciprocal circuit element, and to a communicationdevice.

2. Description of the Related Art

Non-reciprocal circuit elements, such as isolators and circulators, havea characteristic that allows a signal to be transmitted only in apredetermined direction but not in the opposite direction. For example,by utilizing this characteristic, isolators can be used in transmittingcircuits of mobile communication devices, such as automobile telephonesand portable telephones.

Japanese Unexamined Patent Application Publication No. 2005-20195(Patent Document 1) discloses a non-reciprocal circuit element, which isprovided with a permanent magnet having outer peripheral dimensions thatare greater than those of a center-electrode-attached ferrite so that adirect-current magnetic field is distributed uniformly over an entireregion of the ferrite.

However, if non-reciprocal circuit elements of this type are to bemanufactured by cutting out ferrite-magnet assemblies from a mothersubstrate, this manufacturing process is problematic in that it requireshigh costs. Specifically, the manufacturing process involves bondingindividually manufactured center-electrode-attached ferrites accuratelyonto a permanent-magnet/mother substrate, and then cutting the workpieceinto predetermined dimensions.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide a non-reciprocal circuit element which has lowinsertion loss and a simplified manufacturing process, a method formanufacturing the non-reciprocal circuit element, and a communicationdevice.

A preferred embodiment of the present invention provides anon-reciprocal circuit element which includes permanent magnets, aferrite that receives a direct-current magnetic field from the permanentmagnets, a plurality of center electrodes disposed on the ferrite, and acircuit substrate having a terminal electrode on a surface thereof. Thecenter electrodes include a first center electrode and a second centerelectrode defined by conducting films, the first and second centerelectrodes being insulated from each other and intersecting each other,the first center electrode having one end electrically connected to afirst input-output port and the other end electrically connected to asecond input-output port, the second center electrode having one endelectrically connected to the second input-output port and the other endelectrically connected to a third ground port. The permanent magnetshave front and back substantially rectangular principal surfaces, andthe ferrite has front and back substantially rectangular principalsurfaces, the principal surfaces having substantially the samedimensions, the principal surfaces of the permanent magnets beingarranged to face the principal surfaces of the ferrite such thatoutlines of the permanent magnets and an outline of the ferrite coincidewith each other. The ferrite has side surfaces that are substantiallyperpendicular to the principal surfaces thereof, the side surfaces beingprovided with recesses.

In the non-reciprocal circuit element according to this preferredembodiment of the present invention, the center electrodes include thefirst center electrode having one end electrically connected to thefirst input-output port and the other end electrically connected to thesecond input-output port, and the second center electrode having one endelectrically connected to the second input-output port and the other endelectrically connected to the third ground port. Accordingly, a two-portlumped-constant isolator having low insertion loss is provided.

In addition, the permanent magnets have front and back substantiallyrectangular principal surfaces, and the ferrite has front and backsubstantially rectangular principal surfaces, the principal surfacespreferably having substantially the same dimensions, the principalsurfaces of the permanent magnets being arranged to face the principalsurfaces of the ferrite such that the outlines of the permanent magnetsand the outline of the ferrite coincide with each other. Thus, aferrite-magnet assembly can be manufactured by laminating togethermother magnet substrates and a center-electrode-attached mother ferritesubstrate, and then integrally cutting the laminate. This reduces themanufacturing cost.

When the outline dimensions of the permanent magnets are substantiallythe same as the outline dimensions of the ferrite, the direct-currentbias magnetic field applied from the permanent magnets is typicallyweaker in the peripheral areas of the principal surfaces of the ferrite,which face the peripheral areas of the principal surfaces of thepermanent magnets. However, in the non-reciprocal circuit elementaccording to preferred embodiments of the present invention, the sidesurfaces of the ferrite that are substantially perpendicular to theprincipal surfaces thereof (i.e. the peripheral areas of the principalsurfaces of the ferrite where the direct-current bias magnetic field isweaker) are provided with the recesses so that the ferrite itself isreduced. Thus, the amount of ferrite operating under a lowdirect-current bias magnetic field is reduced, thereby reducing lossesof high frequency magnetic flux. In other words, an insertion loss inthe isolator is further reduced. In addition, the ferrite is magneticalthough the direct-current relative magnetic permeability is low,whereas the recesses are of a non-magnetic material, such as Ag and Pd,even with conductors provided therein. Thus, a direct-current magneticflux passing through the peripheral areas of the ferrite is concentratedin regions other than the recesses. Accordingly, this reduces theweakening of the application of the direct-current bias magnetic fieldand provides for an improved distribution of the direct-current biasmagnetic field. In other words, the regions in which the recesses areprovided exhibit an effect that is equivalent to when thedemagnetization factors are locally reduced in the ferrite, whereby thedistribution of direct-current bias magnetic field is improved. As aresult, an insertion loss in the isolator is further reduced.

In the non-reciprocal circuit element according to preferred embodimentsof the present invention, the recesses are preferably provided withintermediate-electrode conductors for electrically connecting theconducting films defining the first center electrode and/or the secondcenter electrode provided on opposite principal surfaces of the ferrite.Furthermore, the recesses are preferably provided withconnector-electrode conductors for electrically connecting the first andsecond center electrodes to the terminal electrode on the circuitsubstrate. If the conductors are to be provided in the recesses in thismanner, it is preferable that the second center electrode be woundaround the ferrite through the opposite principal surfaces and oppositelongitudinal side surfaces thereof by one or more turns, and that thefirst center electrode be wound around the ferrite through the oppositeprincipal surfaces and the opposite longitudinal side surfaces thereofby one or more turns so as to intersect the second center electrode at apredetermined angle. In this case, the conductors in the recesses arepreferably provided only in the longitudinal side surfaces of theferrite, and the ferrite and the permanent magnets are preferablydisposed on the circuit substrate such that the principal surfacesthereof face each other and extend in a direction that is substantiallyperpendicular to the surface of the circuit substrate.

In the non-reciprocal circuit element described above, a high frequencymagnetic flux that is distant from an area surrounded by the secondcenter electrode is guided towards the central portion of the ferritewithout passing through the recesses having the conductors therein. Thismeans that a large number of high frequency magnetic fluxes pass throughthe central portion of the ferrite. Since a sufficient direct-currentbias magnetic field is applied to the central portion of the ferrite, aloss of high frequency magnetic flux is low. As a result, an insertionloss in the isolator is further reduced.

Furthermore, the longitudinal side surfaces of the ferrite arepreferably provided with dummy recesses in addition to the recesses.These dummy recesses may have conductors provided therein. Thisadvantageously produces an improved distribution of direct-current biasmagnetic field in the peripheral areas of the principal surfaces of theferrite, and less losses of high frequency magnetic flux. Moreover, thedummy recesses may have dielectrics embedded therein. Thus, thelongitudinal side surfaces of the ferrite can be made flat.

The recesses and the dummy recesses may be arranged over substantiallythe entire lengths of the opposite longitudinal side surfaces of theferrite at regular intervals. The dummy recesses may each be wider thaneach of the recesses so as to further reduce the amount of high-lossferrite material.

Another preferred embodiment of the present invention also provides amethod for manufacturing a non-reciprocal circuit element includingpermanent magnets, a ferrite that receives a direct-current magneticfield from the permanent magnets, a plurality of center electrodesdisposed on the ferrite, and a circuit substrate having a terminalelectrode on a surface thereof. The method includes forming theplurality of center electrodes in an intersecting manner on front andback principal surfaces of a mother ferrite substrate using conductingfilms such that the center electrodes are insulated from each other,forming a plurality of through holes extending between the front andback principal surfaces, embedding one or more intermediate conductorsinto one or more of the through holes so that the one or moreintermediate conductors electrically connect the conducting filmsdefining the center electrodes, and embedding one or more connectorconductors into one or more of the through holes, the one or moreconnector conductors being electrically connected to the terminalelectrode on the circuit substrate, and forming a laminate bysandwiching the mother ferrite substrate between a pair of mother magnetsubstrates via adhesive layers, and cutting the laminate intopredetermined dimensions along where the through holes are to be cut soas to form a ferrite-magnet assembly having a center-electrode compositesandwiched between a pair of the permanent magnets as a single unit.

The term “through hole” refers to a hole that extends through asubstrate from the front to the back of the substrate and that does notyet have a conductor embedded therein or a conducting layer formedtherein.

In the manufacturing method according to preferred embodiments of thepresent invention, a laminate is formed by sandwiching the motherferrite substrate having the center electrodes and the through holesbetween the mother magnet substrates via the adhesive layers. Thelaminate is then cut into predetermined dimensions along where thethrough holes are to be cut. Consequently, a ferrite-magnet assemblyhaving a center-electrode composite sandwiched between a pair of thepermanent magnets as a single unit is obtained. Accordingly, themanufacturing process is significantly simplified and the manufacturingcost is reduced.

The through holes function as recesses, thereby providing an improveddistribution of direct-current bias magnetic field and less losses ofhigh frequency magnetic flux. One or more of the through holes may beprovided as one or more dummy through holes in which the one or moreintermediate conductors or the one or more connector conductors are notembedded. The one or more dummy through holes may have one or moreconductors embedded therein or one or more dielectrics embedded therein.

Another preferred embodiment of the present invention provides acommunication device including the aforementioned non-reciprocal circuitelement. Accordingly, a communication device with low insertion loss andfavorable electrical properties is obtained.

According to preferred embodiments of the present invention, themanufacturing process is simplified and the insertion loss is furtherreduced. In addition, the distribution of a direct-current bias magneticfield applied to the ferrite is improved, and the losses of highfrequency magnetic flux are reduced.

Other features, elements, steps, characteristics and advantages of thepresent invention will become more apparent from the following detaileddescription of preferred embodiments of the present invention withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded perspective view of a non-reciprocal circuitelement (two-port isolator) according to a preferred embodiment of thepresent invention.

FIG. 2 is a perspective view of a ferrite including center electrodes.

FIG. 3 is a perspective view of the ferrite.

FIG. 4 is an exploded perspective view of a ferrite-magnet assembly.

FIG. 5 is a block diagram showing a circuit configuration in a circuitsubstrate.

FIG. 6 is an equivalent circuit diagram showing a first circuit exampleof the two-port isolator.

FIG. 7 is an equivalent circuit diagram showing a second circuit exampleof the two-port isolator.

FIG. 8 illustrates a direct-current magnetic flux in the ferrite-magnetassembly as viewed transparently.

FIG. 9 illustrates a high frequency magnetic flux in the ferrite asviewed transparently.

FIG. 10 is a perspective view showing another example of thecenter-electrode-attached ferrite.

FIG. 11 illustrates steps included in a manufacturing method accordingto a preferred embodiment of the present invention.

FIG. 12 is a graph showing insertion-loss characteristics of thenon-reciprocal circuit element according to a preferred embodiment ofthe present invention.

FIG. 13 is a block diagram of a communication device according to apreferred embodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of a non-reciprocal circuit element, amanufacturing method therefor, and a communication device according tothe present invention will be described below with reference to theattached drawings.

FIG. 1 is an exploded perspective view of a two-port isolatorcorresponding to a non-reciprocal circuit element according to apreferred embodiment of the invention. The two-port isolator ispreferably a lumped-constant isolator that includes a metallic yoke 10,a cap 15, a circuit substrate 20, and a ferrite-magnet assembly 30constituted by a ferrite 32 and permanent magnets 41.

The yoke 10 is preferably composed of a ferromagnetic material, such assoft iron, and is subjected to an anticorrosive treatment. The yoke 10is arranged as a frame that surrounds the ferrite-magnet assembly 30above the circuit substrate 20. The yoke 10 is preferably formed in thefollowing manner, for example. First, a strip is formed by punching. Inthis state, an engagement portion 10 a is not engaged and the yoke 10 isstill in its unfolded state. A protrusion 11 and a recess 12 are thentightly engaged to each other by so-called crushing so that an annularbody is formed.

Upper surfaces of the ferrite 32 and the permanent magnets 41 have thecap 15 bonded thereto, which is composed of a dielectric material (suchas resin and ceramics). The cap 15 may alternatively be formed of a softmagnetic metallic plate. The yoke 10 and the cap 15 define a magneticcircuit together with the permanent magnets 41, and are plated withsilver over a copper-plated foundation layer to improve theanticorrosive properties and to reduce a conductor loss resulting froman eddy current caused by a high frequency magnetic flux or a conductorloss resulting from a ground current.

As shown in FIG. 2, the ferrite 32 has first and second principalsurfaces 32 a and 32 b which are provided with a first center electrode35 and a second center electrode 36 that are electrically insulated fromeach other. The ferrite 32 has a substantially rectangular prism shape,which includes the first principal surface 32 a and the second principalsurface 32 b that are substantially parallel to each other, longitudinalside surfaces 32 c, 32 d, and lateral side surfaces 32 e, 32 f.

The permanent magnets 41 are bonded to the respective principal surfaces32 a, 32 b with, for example, epoxy adhesive sheet layers 42 (see FIG.4) to form the ferrite-magnet assembly 30, such that a magnetic field isapplied to the principal surfaces 32 a, 32 b of the ferrite 32 in adirection substantially perpendicular to the principal surfaces 32 a, 32b. The permanent magnets 41 have principal surfaces 41 a that havesubstantially the same dimensions as the principal surfaces 32 a, 32 bof the ferrite 32. The principal surfaces 32 a and 41 a are arranged toface each other such that the outlines thereof coincide with each other,and similarly, the principal surfaces 32 b and 41 a are arranged to faceeach other such that the outlines thereof coincide with each other. Amanufacturing process of the ferrite-magnet assembly 30 will bedescribed later in detail with reference to FIG. 11.

As shown in FIG. 2, the first center electrode 35 extends upward from alower right section of the first principal surface 32 a of the ferrite32 and is bifurcated into two segments. The two segments extend in anupper left direction at a relatively small angle with respect to thelongitudinal direction. The first center electrode 35 then extendsupward to an upper left section and turns toward the second principalsurface 32 b through an intermediate electrode 35 a on the upper surface32 c. On the second principal surface 32 b, the first center electrode35 is bifurcated into two segments again so as to overlap with that onthe first principal surface 32 a in the perspective view. One end of thefirst center electrode 35 is connected to a connector electrode 35 bprovided on the lower surface 32 d. The other end of the first centerelectrode 35 is connected to a connector electrode 35 c provided on thelower surface 32 d. The first center electrode 35 is thus wound aroundthe ferrite 32 by one turn. The first center electrode 35 and the secondcenter electrode 36, to be described below, have an insulating filmtherebetween, such that these electrodes intersect each other in aninsulated state.

The second center electrode 36 has a 0.5 th-turn segment 36 a thatextends in the upper left direction from a substantially midsection ofthe lower edge of the first principal surface 32 a at a relatively largeangle with respect to the longitudinal direction and intersects thefirst center electrode 35. The 0.5 th-turn segment 36 a makes a turntowards the second principal surface 32 b through an intermediateelectrode 36 b on the upper surface 32 c so as to connect to a 1 st-turnsegment 36 c. On the second principal surface 32 b, the 1 st-turnsegment 36 c intersects the first center electrode 35 in a substantiallyperpendicular fashion. A lower end portion of the 1 st-turn segment 36 cmakes a turn towards the first principal surface 32 a through anintermediate electrode 36 d on the lower surface 32 d so as to connectto a 1.5 th-turn segment 36 e. On the first principal surface 32 a, the1.5 th-turn segment 36 e extends substantially parallel to the 0.5th-turn segment 36 a and intersects the first center electrode 35. The1.5 th-turn segment 36 e turns toward the second principal surface 32 bthrough an intermediate electrode 36 f on the upper surface 32 c. In asimilar manner, a 2 nd-turn segment 36 g, an intermediate electrode 36h, a 2.5 th-turn segment 36 i, an intermediate electrode 36 j, a 3rd-turn segment 36 k, an intermediate electrode 361, a 3.5 th-turnsegment 36 m, an intermediate electrode 36 n, and a 4 th-turn segment 36o are provided on the corresponding surfaces of the ferrite 32. Theopposite ends of the second center electrode 36 are respectivelyconnected to connector electrodes 35 c and 36 p provided on the lowersurface 32 d of the ferrite 32. The connector electrode 35 c is commonlyused between the ends of the first center electrode 35 and the secondcenter electrode 36.

In other words, the second center electrode 36 is helically wound aroundthe ferrite 32 by four turns. The number of turns is calculated based onthe fact that one crossing of the center electrode 36 across the firstprincipal surface 32 a or the second principal surface 32 b equals a 0.5turn. The intersecting angle between the center electrodes 35, 36 is setso as to adjust the input impedance and insertion loss.

The first and second center electrodes 35, 36 can be modified intovarious shapes. For example, although the first center electrode 35 inthis preferred embodiment is bifurcated into two segments on each of theprincipal surfaces 32 a, 32 b of the ferrite 32, the first centerelectrode 35 does not necessarily need to be bifurcated.

The connector electrodes 35 b, 35 c, 36 p and the intermediateelectrodes 35 a, 36 b, 36 d, 36 f, 36 h, 36 j, 361, 36 n are formed byembedding electrode conductors into corresponding recesses 37 (see FIG.3) provided on the upper and lower surfaces 32 c, 32 d of the ferrite32. In addition, the upper and lower surfaces 32 c, 32 d have dummyrecesses 38 provided substantially in parallel to the electrodes, andare also provided with dummy electrodes 39 a, 39 b, 39 c. Theseelectrodes are formed by preliminarily forming through holes in a motherferrite substrate, embedding electrode conductors into these throughholes, and then cutting the substrate along where the through holes areto be cut. This manufacturing method will be described later. Thesevarious electrodes may alternatively be formed as a conducting film inthe recesses 37, 38.

As a ferrite 32, a YIG ferrite may be used. Alternatively, othersuitable ferrite materials may be used for the ferrite 32. The first andsecond center electrodes 35, 36 and the other various electrodes areeach formed as a thick film composed of silver or a silver alloy by, forexample, printing, transferring, or photolithography. The insulatingfilm between the center electrodes 35 and 36 may be defined by a thickglass dielectric film.

Strontium, barium, or lanthanum-cobalt ferrite magnets are typicallyused as the permanent magnets 41. In contrast to a metallic magnetfunctioning as a conductor, a ferrite magnet is also a dielectric, suchthat a high frequency magnetic flux can be distributed within the magnetwithout loss. For this reason, even if the permanent magnets 41 aredisposed close to the center electrodes 35, 36, deterioration ofelectrical properties, including an insertion loss, is substantiallyprevented. Moreover, the temperature characteristics in the saturationmagnetization of the ferrite 32 and the temperature characteristics inthe magnetic flux density of the permanent magnets 41 are similar.Therefore, with the isolator being defined by a combination of theferrite 32 and the permanent magnets 41, the temperature-dependentelectrical properties of the isolator are satisfactory.

The circuit substrate 20 is a sintered multilayer substrate havingpredetermined electrodes provided on a plurality of dielectric sheets.As shown in FIG. 5, the circuit substrate 20 includes matchingcapacitors C1, C2, Cs1, Cs2, Cp1, Cp2 and a terminating resistor R. Thecircuit substrate 20 also includes terminal electrodes 25 a to 25 e onthe top surface thereof and external-connection terminal electrodes 26,27, 28 on the bottom surface thereof.

The connection relationships among these matching circuit components andthe first and second center electrodes 35, 36 will be described withreference to equivalent circuit diagrams shown in FIGS. 5, 6, and 7. Theequivalent circuit diagram in FIG. 6 shows a first basic circuit examplein the non-reciprocal circuit element (two-port isolator) according to apreferred embodiment of the present invention. The equivalent circuitdiagram in FIG. 7 shows a second circuit example. FIG. 5 illustrates theconfiguration of the second circuit example in FIG. 7.

Specifically, the external-connection terminal electrode 26 provided onthe bottom surface of the circuit substrate 20 functions as an inputport Pl. This terminal electrode 26 is connected to a connection point21 a between the matching capacitor C1 and the terminating resistor Rvia the matching capacitor Cs1. The connection point 21 a is connectedto the one end of the first center electrode 35 via the terminalelectrode 25 a provided on the top surface of the circuit substrate 20and the connector electrode 35 b provided on the lower surface 32 d ofthe ferrite 32.

The other end of the first center electrode 35 and the one end of thesecond center electrode 36 are connected to the terminating resistor Rand the matching capacitors C1, C2 via the connector electrode 35 cprovided on the lower surface 32 d of the ferrite 32 and the terminalelectrode 25 b provided on the top surface of the circuit substrate 20.

On the other hand, the external-connection terminal electrode 27provided on the bottom surface of the circuit substrate 20 functions asan output port P2. This electrode 27 is connected to a connection point21 b between the matching capacitors C2, C1 and the terminating resistorR via the matching capacitor Cs2.

The other end of the second center electrode 36 is connected to thecapacitor C2 and to the external-connection terminal electrodes 28provided on the bottom surface of the circuit substrate 20 via theconnector electrode 36 p provided on the lower surface 32 d of theferrite 32 and the terminal electrode 25 c provided on the top surfaceof the circuit substrate 20. The external-connection terminal electrodes28 function as a ground port P3. Furthermore, the external-connectionterminal electrodes 28 are also connected to the yoke 10 via theterminal electrodes 25 d, 25 e provided on the top surface of thecircuit substrate 20.

A connection point between the input port P1 and the capacitor Cs1 isconnected to an impedance-adjusting capacitor Cp1 that is connected toground. Likewise, a connection point between the output port P2 and thecapacitor Cs2 is connected to an impedance-adjusting capacitor Cp2 thatis connected to ground.

The circuit substrate 20 and the yoke 10 are combined with each other bysoldering them together through the terminal electrodes 25 d, 25 e andother dummy electrodes. The electrodes on the lower surface 32 d of theferrite 32 in the ferrite-magnet assembly 30 are bonded to the terminalelectrodes 25 a, 25 b, 25 c and other dummy terminal electrodes on thecircuit substrate 20 by soldering, and the lower surfaces of thepermanent magnets 41 are bonded on the circuit substrate 20 with anadhesive. A one-part or two-part epoxy adhesive of a thermosetting typeis suitable for this adhesive. In other words, using both solder andadhesive for the bonding between the ferrite-magnet assembly 30 and thecircuit substrate 20 ensures a secure connection.

The circuit substrate 20 may be a substrate formed by firing a mixtureof glass and alumina or other dielectric materials or may be a compositesubstrate composed of resin or glass and other dielectric materials. Theinternal and external electrodes may each be formed of, for example, athick film composed of silver or a silver alloy, a thick film composedof copper, or a copper foil. In particular, the external-connectionterminal electrodes are preferably plated with gold over a nickel-platedlayer. This is to improve the anticorrosive properties and theresistance to solder leaching, and to prevent the strength of thesoldered sections from being reduced due to various causes.

In the two-port isolator described above, one end of the first centerelectrode 35 is connected to the input port P1 and the other end thereofis connected to the output port P2, and one end of the second centerelectrode 36 is connected to the output port P2 and the other endthereof is connected to the ground port P3. Consequently, a two-portlumped-constant isolator with a low insertion loss is provided.Moreover, when the isolator is in operation, a large magnitude of highfrequency current flows into the second center electrode 36, whereasvery little high frequency current flows into the first center electrode35. Accordingly, the direction of high frequency magnetic field producedby the first center electrode 35 and the second center electrode 36 isdetermined based on the position of the second center electrode 36. Thedetermination of the direction of high frequency magnetic fieldfacilitates the measures for further reducing an insertion loss.

The permanent magnets 41 have front and back rectangular principalsurfaces 41 a, and the ferrite 32 has front and back substantiallyrectangular principal surfaces 32 a, 32 b, the principal surfaces 32 a,32 b, 41 a having substantially the same dimensions. The principalsurfaces 32 a and 41 a are arranged to face each other such that theoutlines thereof coincide with each other, and similarly, the principalsurfaces 32 b and 41 a are arranged to face each other such that theoutlines thereof coincide with each other. Therefore, as will bedescribed later with reference to FIG. 11, the ferrite-magnet assemblies30 can be manufactured by laminating together mother magnet substratesand a center-electrode-attached mother ferrite substrate and thenintegrally cutting the laminate. This reduces the manufacturing cost.The principal surfaces 32 a, 32 b, 41 a are arranged substantiallyvertically on the circuit substrate 20 in a direction that issubstantially perpendicular to the surface of the circuit substrate 20.Moreover, the side surfaces of the permanent magnets 41 and the ferrite32, namely, the surfaces mounted to the circuit substrate 20 are flushwith each other. Consequently, this improves the reliability of theconnection with the terminal electrodes on the circuit substrate 20. Inaddition, even if the permanent magnets 41 are made thicker to obtain alarge magnetic field, the height will not be increased regardless of thethickness.

When the outline dimensions of the permanent magnets 41 aresubstantially the same as the outline dimensions of the ferrite 32 asshown in FIG. 8, the direct-current bias magnetic field applied from thepermanent magnets 41 is generally weaker in the peripheral areas of theprincipal surfaces 32 a, 32 b of the ferrite 32, which face theperipheral areas of the principal surfaces 41 a of the permanent magnets41. However, in the isolator according to a preferred embodiment of thepresent invention, the side surfaces 32 c, 32 d that are substantiallyperpendicular to the principal surfaces 32 a, 32 b of the ferrite 32(i.e. the peripheral areas of the principal surfaces 32 a, 32 b of theferrite 32 where the direct-current bias magnetic field is weaker) areprovided with the recesses 37, 38 so that the ferrite 32 itself isreduced. This inhibits the direct-current bias magnetic field fromweakening and enables less losses of high frequency magnetic flux. Inother words, an insertion loss in the isolator is further reduced. Inaddition, the ferrite 32 is magnetic although the direct-currentrelative magnetic permeability is low, whereas the recesses 37, 38 arenon-magnetic even with the conductors provided therein. Thus, adirect-current magnetic flux passing through the recesses 37, 38 has atendency to concentrate in regions other than the recesses. Accordingly,this prevents the weakening of application of the direct-current biasmagnetic field and enables an improved distribution of thedirect-current bias magnetic field. In other words, the regions at whichthe recesses 37, 38 are provided exhibit an effect that is equivalent toa case in which the demagnetization factors are locally reduced in theferrite 32. As a result, an insertion loss in the isolator is furtherreduced. This effect can similarly occur in a case in which conductorsare not provided in the recesses 37, 38.

The conductors in the recesses 37, 38 are provided only on thelongitudinal side surfaces 32 c, 32 d of the ferrite 32. The lateralside surfaces 32 e, 32 f are surfaces through which a high frequencymagnetic flux that is substantially perpendicular to the second centerelectrode 36 passes. A high frequency magnetic flux is allowed to passwithout being inhibited as long as there are no conductors provided inthese side surfaces 32 e, 32 f. However, providing the conductors on theside surfaces 32 e, 32 f will not be problematic as long as theconductors are in the corner regions of the side surfaces 32 e, 32 f. Inthat case, a high frequency magnetic flux is allowed to pass withoutsubstantially being inhibited.

The dummy recesses 38 are not necessarily required. FIG. 10 shows acenter-electrode-attached ferrite 32 in which the dummy recesses 38 areomitted.

A high frequency magnetic flux that is distant from an area surroundedby the second center electrode 36 generally begins to immediatelyspread, causing multiple high frequency magnetic fluxes to diffuse fromthe ferrite 32. In contrast, in the isolator according to preferredembodiments of the present invention, since the intermediate electrodesand connector electrodes are provided in the recesses 37, 38, the highfrequency magnetic flux is guided towards the central portion of theferrite 32 without passing through the recesses 37, 38 having theconductors therein, as shown in FIG. 9. This means that a large numberof high frequency magnetic fluxes pass through the central portion ofthe ferrite 32. Since a sufficient direct-current bias magnetic field isapplied to the central portion of the ferrite 32, a loss of highfrequency magnetic flux is low. As a result, an insertion loss in theisolator is further reduced.

Since conductors are embedded in the dummy recesses 38 provided in thelongitudinal side surfaces 32 c, 32 d of the ferrite 32, theaforementioned advantage significantly contributes to an improveddistribution of direct-current bias magnetic field in the peripheralareas of the principal surfaces 32 a, 32 b of the ferrite 32 and to lesslosses of high frequency magnetic flux. As an alternative to embeddingconductors in the recesses 37 and the dummy recesses 38, conductingfilms may be formed by thick film processing or thin film processing.Furthermore, the dummy recesses 38 may have dielectrics materialembedded therein. Thus, the longitudinal side surfaces 32 c, 32 d of theferrite 32 can be made flat. Furthermore, the dummy recesses 38 may bewider than the recesses 37 so as to further reduce the amount ofhigh-loss ferrite material.

It is possible to prevent the insertion loss from increasing byconfiguring the principal surfaces 41 a of the permanent magnets 41 tohave a size greater than the principal surfaces 32 a, 32 b of theferrite 32. However, this not only reduces the advantage of being ableto cut the mother magnet substrates and the mother ferrite substratesimultaneously in the manufacturing process, but also leads to anincreased surface area of the permanent magnets 41. Thus, when theferrite-magnet assembly 30 is disposed vertically on the circuitsubstrate 20, the isolator has an increased height, and the lowersurface 32 d of the ferrite 32 is in a raised state from the frontsurface of the circuit substrate 20. This makes the connection betweenthe various electrodes and the terminal electrodes more difficult,resulting in reduced connection reliability.

Furthermore, in the isolator according to preferred embodiments of thepresent invention, the first center electrode 35 is wound by one turnand the second center electrode 36 is wound by four turns, wherebyfavorable insertion loss is obtained over a wide band. In other words,by winding the first and second center electrodes 35, 36 around theferrite 32, the number of intersections between the center electrodes35, 36 increases, and the coupling coefficient between the centerelectrodes 35, 36 is increased. This enables less insertion loss and awider band for the passing frequency.

Furthermore, as shown in the second circuit example (see FIG. 7), thematching capacitor Cs1 is interposed between the input port P1 and theconnection point 21 a of the first center electrode 35 and the matchingcapacitor C1, and the matching capacitor Cs2 is interposed between theoutput port P2 and the connection point 21 b of the center electrodes35, 36. Thus, when the inductance of the center electrodes 35, 36 is setat a large value and the electrical properties in a wide band areimproved, the impedance (about 50Ω) with respect to a device connectedto the isolator can be adjusted. This advantage can be similarlyachieved by including only one of the matching capacitors Cs1 and Cs2.

By incorporating a matching inductor between the ground port P3 and aconnection point of the second center electrode 36 and the capacitor C2,a predetermined high frequency wave, such as a second or third harmonicwave, is suppressed. Furthermore, LC series circuits defined byinductors and capacitors may be incorporated between the input port P1and the ground and between the output port P2 and the ground. Byproviding these LC series circuits, a predetermined high frequency wave,such as a second or third harmonic wave, is similarly suppressed.

The ferrite 32 and the pair of permanent magnets 41 are combined witheach other via the adhesive sheet layers 42. Thus, the isolator ismechanically stable and has a rigid structure that is prevented frombecoming deformed or broken in response to vibration or shock. Thisisolator is suitable for a portable communication device. Instead ofusing the adhesive sheet layers 42 for combining the ferrite 32 and thepermanent magnets 41, other various alternatives can be used. Onealternative example is to apply an adhesive agent.

Since the center electrodes 35, 36 are formed as conducting films on theprincipal surfaces 32 a, 32 b of the ferrite 32, these electrodes areformed with stability and high precision, thereby enabling massproduction of the isolators having uniform electrical properties. Inaddition, by using a film of sintered glass powder for the insulatingfilm between the center electrodes 35 and 36, the principal surfaces 32a, 32 b of the ferrite 32 can have a high degree of flatness as comparedto when the center electrodes are formed of metal sheets. As a result,the ferrite 32 and the pair of permanent magnets 41 can be combined witha high degree of parallelism with respect to the positional relationshiptherebetween.

In the isolator according to preferred embodiments of the presentinvention, the circuit substrate 20 is a multilayer dielectricsubstrate. Thus, circuitry including capacitors and inductors can becontained within the substrate, so that a compact and low-profilestructure of the isolator is achieved. Moreover, the circuit componentsare connected to each other within the substrate, thereby improving thereliability. The circuit substrate 20 does not necessarily need to be amultilayer structure, and may alternatively be in the form of asingle-layer structure. In that case, the circuit substrate 20 may havechip-type capacitors externally attached thereto.

A manufacturing process of the ferrite-magnet assembly 30 will now bedescribed. When manufacturing the ferrite-magnet assembly 30, the centerelectrodes 35, 36 are formed on front and back surfaces of a motherferrite substrate using conducting layers, such that these electrodesare insulated from each other and intersect each other. Moreover, aplurality of through holes extending between the front and back surfacesis formed. An intermediate electrode material and a connector electrodematerial are embedded in the corresponding through holes.

Subsequently, a laminate is formed by sandwiching the mother ferritesubstrate between a pair of mother magnet substrates via an adhesive.The laminate is cut into predetermined dimensions along where thethrough holes are to be cut. As a result, a ferrite-magnet assembly 30having the center-electrode-attached ferrite 32 sandwiched between apair of permanent magnets 41 as a single unit is obtained.

FIG. 11 illustrates the process. In steps 1, 2, and 3, an adhesive sheetlayer 42 having a separator 415 attached thereto is bonded to a mothermagnet substrate 411. The separator 415 is then peeled off. In step 4, amother ferrite substrate 322 (having center electrodes and throughholes) is hermetically bonded on the mother magnet substrate 411 via theadhesive sheet 42. In steps 5 and 6, another mother magnet substrate 411having an adhesive sheet layer 42 is hermetically bonded onto the motherferrite substrate 322. As a result, a laminate 400 is obtained.

In step 7, the laminate 400 is bonded onto a dicing tape 416. In step 8,using a dicer, the laminate 400 is cut into predetermined dimensionsalong where the through holes are to be cut, whereby a plurality offerrite-magnet assemblies 30 is obtained, each being a single unit.

According to the aforementioned steps, the ferrite-magnet assemblies 30,each including the permanent magnets 41 of substantially the same sizethat sandwich the ferrite 32 of the same size therebetween, can bemanufactured efficiently with high precision, thereby significantlyreducing the cost. The advantages of these ferrite-magnet assemblies 30have been described above.

In particular, because the mother magnet substrates 411 and the motherferrite substrate 322 having large surface areas are used, the degree ofparallelism among the permanent magnets 41 and the ferrite 32 isimproved as compared to a case in which the permanent magnets 41 and theferrite 32 are individually bonded together. Thus, the parallelism anduniformity of a bias magnetic field applied to the ferrite 32 areassured, thereby preventing deterioration of electrical properties, suchas an insertion loss. In addition, displacement of the ferrite 32 isprevented from occurring. This not only prevents individual differencesamong the isolators, but also provides highly reliable isolators withreduced time/age deterioration.

FIG. 12 shows electrical properties of isolators in accordance withconfigurations of the ferrite-magnet assembly 30. Each of the isolatorsmeasured for electrical properties includes the ferrite-magnet assembly30. Specifically, with regard to the principal surfaces of the ferrite32 and the permanent magnets 41, the longitudinal sides preferably havea length of about 2.0 mm and the lateral sides have a length of about0.60 mm, for example. The ferrite 32 has a thickness of about 0.125 mm.The permanent magnets 41 have a thickness of about 0.35 mm.

In FIG. 12, a curve line A shows insertion-loss characteristics of anisolator equipped with a ferrite-magnet assembly 30 having conductorsembedded in the dummy recesses 38.

When the permanent magnets 41 are replaced with permanent magnets whoseprincipal surfaces have 2.4 -mm longitudinal sides and 0.90 -mm lateralsides and whose thickness is 0.35 mm such that these permanent magnetshave a greater surface area than the ferrite 32, the insertion-losscharacteristics are substantially the same as the insertion-losscharacteristics shown with the curve line A. However, this unfavorablycauses the height of the isolator to be increased by about 0.3 mm. Inother words, the insertion-loss characteristics obtainable with theaforementioned ferrite-magnet assembly 30 are equivalent to theinsertion-loss characteristics obtained when using permanent magnets 41that have a size greater than the ferrite 32.

A curve line B shows insertion-loss characteristics of an isolatorequipped with a ferrite-magnet assembly 30 having dielectrics (glass)embedded in the dummy recesses. A curve line C shows insertion-losscharacteristics of an isolator equipped with a ferrite-magnet assembly30 having the center-electrode-attached ferrite 32 (see FIG. 10) withoutthe dummy recesses 38.

By comparing the curve lines A, B, and C, it is apparent that the curveline A has the lowest insertion loss. The curve line B is higher thanthe curve line A by about 0.02 dB, and the curve line C is higher thanthe curve line A by about 0.05 dB. However, all of these curve lines A,B, and C show favorable electrical properties.

A portable telephone will now be described as an example of acommunication device according to preferred embodiments of the presentinvention.

FIG. 13 is an electric-circuit block diagram of an RF portion of aportable telephone 220. In FIG. 13, reference numeral 222 denotes anantenna element, reference numeral 223 denotes a duplexer, referencenumeral 231 denotes a transmitting-side isolator, reference numeral 232denotes a transmitting-side amplifier, reference numeral 233 denotes atransmitting-side interstage bandpass filter, reference numeral 234denotes a transmitting-side mixer, reference numeral 235 denotes areceiving-side amplifier, reference numeral 236 denotes a receiving-sideinterstage bandpass filter, reference numeral 237 denotes areceiving-side mixer, reference numeral 238 denotes a voltage-controlledoscillator (VCO), and reference numeral 239 denotes a local bandpassfilter.

The two-port isolator according to a preferred embodiment describedabove can be used as the transmitting-side isolator 231. Theinstallation of the isolator enables favorable electrical properties.

The non-reciprocal circuit element, the manufacturing method therefor,and the communication device according to the present invention are notlimited to the preferred embodiments described above, and variousmodifications are permissible within the scope and spirit of theinvention.

For example, by inverting the N-pole and the S-pole of the permanentmagnets 41, the input port P1 and the output port P2 can be switched.Furthermore, although the matching circuit components are all includedin the circuit substrate in the above preferred embodiments, the circuitsubstrate may alternatively have chip-type inductors or capacitorsexternally attached thereto.

In the above preferred embodiments, the principal surfaces in theferrite-magnet assembly are arranged substantially perpendicular to thecircuit substrate, or in other words, substantially vertically on thecircuit substrate. Alternatively, the principal surfaces may be arrangedsubstantially parallel to the circuit substrate, or in other words,substantially horizontally on the circuit substrate.

Accordingly, the present invention provides a non-reciprocal circuitelement, such as an isolator and a circulator, which is particularlyadvantageous in view of achieving a simplified manufacturing process anda reduced insertion loss.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing the scope andspirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A non-reciprocal circuit element comprising: permanent magnets; aferrite arranged to receive a direct-current magnetic field from thepermanent magnets; a plurality of center electrodes disposed on theferrite; and a circuit substrate having a terminal electrode on asurface thereof; wherein the center electrodes include a first centerelectrode and a second center electrode including conducting films, thefirst and second center electrodes being insulated from each other andintersecting each other, the first center electrode having one endelectrically connected to a first input-output port and the other endelectrically connected to a second input-output port, the second centerelectrode having one end electrically connected to the secondinput-output port and the other end electrically connected to a thirdground port; the permanent magnets have front and back substantiallyrectangular principal surfaces, and the ferrite has front and backsubstantially rectangular principal surfaces, the principal surfaces ofthe permanent magnets and the ferrite having substantially the samedimensions, the principal surfaces of the permanent magnets beingarranged to face the principal surfaces of the ferrite such thatoutlines of the permanent magnets and an outline of the ferrite coincidewith each other; and the ferrite has side surfaces that aresubstantially perpendicular to the principal surfaces thereof, the sidesurfaces being provided with recesses.
 2. A communication devicecomprising the non-reciprocal circuit element to claim
 1. 3. Thenon-reciprocal circuit element according to claim 1, wherein therecesses are provided with intermediate-electrode conductors arranged toelectrically connect the conducting films defining at least one of thefirst center electrode or the second center electrode provided on theopposite principal surfaces of the ferrite.
 4. The non-reciprocalcircuit element according to claim 3, wherein the second centerelectrode is wound around the ferrite through the opposite principalsurfaces and opposite longitudinal side surfaces thereof by at least oneturn; the first center electrode is wound around the ferrite through theopposite principal surfaces and the opposite longitudinal side surfacesthereof by at least one turn so as to intersect the second centerelectrode at a predetermined angle; the conductors in the recesses areprovided only in the longitudinal side surfaces of the ferrite; and theferrite and the permanent magnets are disposed on the circuit substratesuch that the principal surfaces thereof face each other and extend in adirection substantially perpendicular to the surface of the circuitsubstrate.
 5. The non-reciprocal circuit element according to claim 3,wherein the longitudinal side surfaces of the ferrite are provided withdummy recesses in addition to the recesses.
 6. The non-reciprocalcircuit element according to claim 5, wherein the dummy recesses havedielectrics embedded therein.
 7. The non-reciprocal circuit elementaccording to claim 5, wherein the recesses and the dummy recesses arearranged over substantially the entire lengths of the oppositelongitudinal side surfaces of the ferrite at regular intervals.
 8. Thenon-reciprocal circuit element according to claim 5, wherein each of thedummy recesses are wider than each of the recesses.
 9. Thenon-reciprocal circuit element according to claim 5, wherein the dummyrecesses have conductors provided therein.
 10. The non-reciprocalcircuit element according to claim 1, wherein the recesses are providedwith connector-electrode conductors for electrically connecting thefirst and second center electrodes to the terminal electrode on thecircuit substrate.
 11. The non-reciprocal circuit element according toclaim 10, wherein the second center electrode is wound around theferrite through the opposite principal surfaces and oppositelongitudinal side surfaces thereof by at least one turn; the firstcenter electrode is wound around the ferrite through the oppositeprincipal surfaces and the opposite longitudinal side surfaces thereofby at least one turn so as to intersect the second center electrode at apredetermined angle; the conductors in the recesses are provided only inthe longitudinal side surfaces of the ferrite; and the ferrite and thepermanent magnets are disposed on the circuit substrate such that theprincipal surfaces thereof face each other and extend in a directionsubstantially perpendicular to the surface of the circuit substrate. 12.The non-reciprocal circuit element according to claim 10, wherein thelongitudinal side surfaces of the ferrite are provided with dummyrecesses in addition to the recesses.
 13. The non-reciprocal circuitelement according to claim 12, wherein the dummy recesses havedielectrics embedded therein.
 14. The non-reciprocal circuit elementaccording to claim 12, wherein the recesses and the dummy recesses arearranged over substantially the entire lengths of the oppositelongitudinal side surfaces of the ferrite at regular intervals.
 15. Thenon-reciprocal circuit element according to claim 12, wherein each ofthe dummy recesses are wider than each of the recesses.
 16. Thenon-reciprocal circuit element according to claim 12, wherein the dummyrecesses have conductors provided therein.